These people really should just use Stacker News. $20 minimums are a little rich for replies, but since they're using Stripe I imagine anything less means the processors get it all.
Radiopaper lets you pay other users for their writing. To do this, you can find someone whose writing you’d want to pay for. Maybe it’s a journalist, or an author, or an acquaintance with a really good idea. You can pay $20 or more (up to $10,000) to attach a commission for that user to one of your posts, and they’ll be paid once they’ve replied. Radiopaper will collect 10% of these commissions.
Also, they don't even show it when the feature is used!
The only users who know about the commission are the sender and the receiver. Radiopaper doesn’t indicate to anyone else that the message was paid for.
And they have this functionality:
You can make a new post on Radiopaper whenever you want. When someone replies to one of your posts, it starts out as a private message between you and them. You get to decide whether to publish that reply — that is, allow everyone else to see it — or ignore it.
The idea of sending a bounty to specific user to reply to one of your posts is kinda cool, though.
Or just the idea of attaching bounties to the specific user you would like to complete them...